Gas turbine engines are provided with fan blades and rotor disks. The fan blades may experience vibrations that increase fatigue. The growing amplitude of vibrations can be a result of an aeromechanical instability that is referred to as flutter. The fan blades are designed to have a positive aero damping, which depends on flow conditions, mode frequency, and nodal diameters. Two methods are traditionally used to increase aerodynamic damping. First, the fan blade is shaped to control the aerodynamic loading. For example, the tip blade loading may be minimized by reducing the incidence angle near the blade tip and increasing the loading away from OD. Second, the blade external geometry is modified to tune natural frequency and mode-shape, such as modifying blade thickness, leading and trailing edge thicknesses, attachment shape, and changing the chord length. Sometimes structural changes may be applied to alternating fan blades or installing fan blades in a pattern around the rotor disk in order to mistune the rotor. This intentional mistuning can be used as a tool to reduce the amplitude of vibration in the fan blades.
Accordingly, it is desirable to change blade frequency to achieve mistuning to reduce the amplitude of vibration in the fan blades.